This invention relates to a device for selecting the hooks of a shed-forming device for a weaving machine, comprising a number of upwardly and downwardly movable hooks and, for each hook, a selection element with which the hook can be selected in order to be held by a holding element at a selection height and a returning means in order to exert a downward directed returning force on a contact part of the hook that is lower than the top hook extremity, only in the course of a part of the movement path of the hook.
This invention also relates to a shed-forming device provided with a number of these selection devices, more specifically a jacquard machine, as well as a weaving machine provided with such a shed-forming device.
When weaving on a weaving machine, in successive operating cycles of the weaving machine, one or several weft yarns are inserted in a shed between warp yarns. The insertion of weft yarns occurs in each case at well-defined weft insertion levels. In the course of the weaving, in each operating cycle, the various warp yarns have to be brought into a predetermined position in relation to each weft insertion level in order to obtain the desired fabric. Devices with which warp yarns can automatically be correctly positioned in the course of weaving on a weaving machine, are generally known. In the claims and the specification of this patent application such a device is called a shed-forming device.
Jacquard machines with which the warp yarns can be positioned individually or in groups in the course of weaving on a weaving machine, are known. A known jacquard machine comprises a number of shed-forming devices with two knives moving up and down in opposite phase that can each engage a series of hooks. For this purpose each hook has a supporting nose that is provided in order to rest on a supporting edge of a knife. This machine furthermore also comprises a number of selection elements with solenoids with which each hook can be brought into a position whereby a hook-shaped projection provided at a fixed height arrives in an opening of the hook, so that this hook remains hanging at a selection height during the further movements of the knives. This hook is then selected. The hook can remain selected during several operating cycles of the knives, but can also be already released on the following movement cycle of the knives by a suitable control of the selection element in question, whereby the hook-shaped projection no longer meshes in the opening of the hook, and whereby the hook again rests with its supporting nose on a knife and moves downward with the knife.
The movements of the hooks can, for example with pulley devices, be transmitted to harness cords, which in their turn are connected to jacquard heddles that can more one or several warp yarns. By selecting hooks or not the jacquard heddles, and therefore also the warp yarns, can be brought into two or more different positions. The selection elements can for example be electronically operated in order at each operating cycle of a weaving machine, to obtain a correct positioning of the warp yarns, through a suitable hook selection.
A jacquard heddle is lifted upward by a jacquard hook that rests on an upward moving knife. When a jacquard heddle has to be brought to a lower situated position a jacquard hook working together therewith will follow the downward movement of a knife. In order to hold each hook on the knife with these up and down movements, each jacquard heddle is connected to a return spring that exerts a downward directed force on the jacquard heddle.
With selection of a hook it is of great importance that the hook is brought to the correct height at the right moment in order to be able to implement this selection without any problem, and that the hook, after implementing the selection, hooks in well on the hook-shaped projection, or, in case of non-selection thereof, moves down again on a knife. The spring force acting on the jacquard heddles often appears to be insufficiently effective for this purpose. A number of devices are known with which it has been attempted to remedy this. These devices have the characteristics that are mentioned in the first paragraph of this specification.
A first known device is the one according to the patent publication DD 283 429. In this device a second return spring is provided for safely bringing the hook to the selection position were for one reason or another the first return spring (that acts on the jacquard heddle) not to do this, e.g. knots entangling in the warp yarns. This device also has the great disadvantage that a second spring has to be compressed over the total lifting height of the hooks. The drive of this device will therefore consume a higher power.
A second device is known from patent publication EP 0 408 076. With this device a pressure bar is provided that only presses on the hooks if these are in the top part (in the vicinity of their top dead point) of their movement path. The weight of the pressure bar is sufficient in order to prevent the hook from leaving the knife upon reaching the top dead point of the movement, and in order to press downward a magnetically attracted hook against the friction, until it hangs on the projection, even were the return force acting on the jacquard heddles have failed entirely. This device has the characteristics mentioned in the first paragraph of this specification but has as disadvantage that the removal of a hook is rather time-consuming and that the device is not suitable for high weaving speeds.
Another solution is known from patent publication EP 0 823 501. This device can only operate with jacquard machines with rather thick-walled form-retaining plastic hooks.
The purpose of this invention is to provide a hook selection device with which the above described disadvantages are remedied, and with which therefore an operationally safe hook selection can be implemented at relatively high weaving speeds, whereby the hooks are removable, and whereby the hook selection device requires very limited additional power.
In particular by an operationally safe hook selection a selection is meant that is implemented without any problem and continues to be maintained, even were the return force of the jacquard heddle would be reduced temporary or cease entirely.
This purpose is achieved according to this invention by providing a hook selection device with the characteristics mentioned in the first paragraph of this specification, of which each returning device comprises a pressure means that can be moved upwards by a hook against a downward directed spring load.
If a resetting force is exerted on the top hook extremity, a non-form-retaining hook will deform under the influence of this force and the hook selection will fail. By applying a smaller return force the chance of deformation of the hook is reduced but the smaller return force therefore also becomes less effective.
If however the return force makes contact on a lower situated contact part of the hook, the point of application of the return force acting on the hook will lie either at a shorter distance above the supporting nose of the hook or below this supporting nose. The power of the forces acting on a hookxe2x80x94namely the downward directed return force and the upward directed pushing force of the knife on which the hook rests applied to the supporting nosexe2x80x94in order to deform the hook decreases because of this, so that an effective return force can also be acting on non-form-retaining hooks without risk of an undesired deformation of the hook. In contrast to a number of known devices this selection device is therefore very well suited for use with hooks that are not form-retaining. Such hooks are usually made out of metal and are among others used with selection devices that operate with solenoids, whereby the hooks have to be capable of being bent under the influence of a magnetic attractive or repulsive force developed by a solenoid in order to come into a selection position or a non-selection position.
Since the return force only has to be acting during a limited part of the movement path of the hooks, the selection device can be so implemented that the hooks are easily removable. The hooks also only have to be moved during a limited part of their movement path against the return force so that the additional power that is consumed by this device is minimal.
This selection device also ensures a very operationally safe selection. Through the return force the hooks are prevented from leaving the knife at the moment that they can be selected and it is ensured that the holding means provided on the hook is correctly positioned in relation to the holding element. This is especially necessary where the hooks can be selected in the vicinity of the top dead point of their up and down movement. After the selection has been implemented and the holding element in co-operation has come with the holding means provided on the hook (e.g. if the hook is brought into a bent position by the selection element, so that a hook-shaped projection provided at a fixed height latches in a window opening of the hook), the return force ensures that the hook with the downward movement of the knife is pressed downward over a short distance, so that the co-operation between holding element and holding means is improved. Where the holding element and holding means are respectively implemented as a projection and an opening (of vice versa) this results in the correct hooking-up of the hook.
The return force continues to be maintained as long as the hook remains hooked up. A temporary interruption in the downward force exerted on the jacquard heddle will therefore not lead to a hook falling off. When a hook is no longer selected, the returning force will also ensure that the xe2x80x9cstick-slipxe2x80x9d effect is better overcome and that the hook at least starts to follow the downward movement of the knife.
Once in movement the force acting on the jacquard heddle must be sufficient in order to hold the hook on the knife during the remainder of the downward movement.
Because of the fact that each return device comprises a pressure means, which is upwardly movable by a hook against a downward directed spring pressure, the selection device is very reliable and is less subject to wear and tear than the known devices.
Because of this the device can also operate at a very high speed and the pre-tensioning of the resetting springs in the harness (that exerts a downward directed spring pressure on the jacquard heddles) is reduced. This leads to a saving in the drive power of the jacquard machine.
The hook selection device according to this invention is preferably so implemented that the aforesaid contact part of each hook lies lower than the holding means with which a holding element can work together in order to hold the hook at the selection height. The deforming power of the forces acting on a flexible hook is still further reduced because of this so that the device can work operationally safely with hooks with a great flexibility.
Each return device can be provided for that purpose with a pressure means that, only in the course of the upward movement of this hook, can be moved upward on a top part of its movement path. Because of this the return force is acting on the hooks when these are in the top dead point of their up and down movement. Because of this the hooks are prevented from leaving the knife in that top dead point through their inertia, and not being correctly positioned in relation to the holding element and/or the selection element.
In a preferred embodiment of the hook selection device according to this invention each return device comprises a guide for guiding the pressure means in the course of its up and down movements.
A particularly simple and effective embodiment is obtained if the aforesaid guide comprises a guiding wall that to a great extent encloses the pressure means, while the aforesaid contact part of the hook in the course of the up and down movements of the hook extends inside the guiding space enclosed by the guiding wall, so that the contact part can take the pressure means along upward.
Each return device can for example comprise a spring disposed between the top of the pressure means and an immovable bearing surface that exerts a downward directed spring pressure on the pressure means. This spring is preferably provided in a top part of the guiding space.
The hooks can be of very simple design if the contact part is a lateral projection of the hook that is at the same time provided in order to rest on a lifting means. The hooks need not then be provided with a separate contact part.
Each hook can be so implemented that it comprises a supporting nose that is provided in order to rest on a lifting means, while the contact part of each hook is a(nother) lateral projection of the hook, whereby this supporting nose and this contact means are provided opposite each other on either side of the hook.
Preferably, the hooks are provided in order to be bent under the influence of a force exerted by a selection element.
In a particular embodiment each return device is provided in a lower part of a guide housing for the jacquard hooks. The device is most effective when a return device is provided for each hook.
A shed-forming device, in particular an electronically operated jacquard machine, which is provided with or works together with a hook selection device according to this invention, as well as a weaving machine provided with such a shed-forming device, falls within the scope of protection determined by the claims of this patent application.
In the following detailed specification of an embodiment example of a hook selection device according to this invention the aforesaid characteristics and advantages of the invention are further explained and additional properties and advantages thereof are indicated. The purpose of this specification is only to give a clarifying example of a possible embodiment of this invention and can therefore in no way be interpreted as a restriction on the field of application of the invention or on the patent rights claimed in the claims.
In this specification reference is made by means of reference numbers to the figures attached hereto, of which